A typical printed circuit board is a flat board that provides support and electrical interconnection between microchips and other electronic components. The base of the board can be made of reinforced fiberglass or plastic, and the electronic components are elezctrically interconnected by conductive pathways. There are several ways to make printed circuit boards. One method entails bonding a conductive foil, such as copper, over the base. A conductive pattern is then formed in the conductor. One method of patterning the metal layer uses a negative image of the desired circuit pattern and a photo resist layer. The photo resist is activated using the image such that selected areas of the photo resist can be removed. An etch process is then performed to remove the photo resist that was not activated and the underlying metal layer, leaving behind the conductive pathway pattern.
Today, most printed circuit boards are composed of several sheets or layers. A multi-layer printed circuit board may be fabricated from several composite sheets, each comprising a substrate of insulating material and a layer of metal, such as copper, attached to one surface of the substrate using a resin. A desired conductive pathway pattern is then provided in the metal layer, as explained, and multiple layers of insulating material and metal conductor layers can be fabricated. A soldermask layer can be provided over the top level of conductor to control areas exposed to a soldering process. A finished printed circuit board can then put through an assembly process where it is populated with various electrical components.
Delamination, or separation, problems have been discovered in the printed circuit board assembly industry regarding processes similar to the one described above. These problems are a result of the various environmental stresses inherent to assembly procedures. For example, delamination of the soldermask layer can occur when moisture retained by a board's constituent components are exposed to post-production assembly processes performed at high temperatures.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need for a multi-layer printed circuit board assembly that reduces the likelihood of delamination.